Brain Pathology Case of the Month - October 2002

DIAGNOSIS: RASMUSSEN'S CHRONIC ENCEPHALITIS SYNDROME

DISCUSSION:

Rasmussen's encephalitis is a chronic neurological disorder, first described in 1958, characterized by intractable seizures, slowly progressive neurological deficits involving one hemibody, and encephalitis typically confined to one hemisphere (1). The age of onset is between 1 and 14 years with the development of frequent partial and generalized seizures; 56% of patients develop epilepsia partialis continua. A progressive neurological decline follows with hemiparesis, hemisensory deficits, hemianopsia, and speech deficits, if the dominant hemisphere is involved, and ultimately dementia. The active neurological decline lasts from 1 to 20 years and the patients then remain stable with a fixed neurological deficit and residual seizures (2).

Pathological examination shows a chronic encephalitis confined to one hemisphere. In the active phase, neuronophagia, activated microglial cells (rod cells) and microglial nodules, and perivascular lymphocytic infiltrates, are present. In the more chronic phase neuronal loss and gliosis predominate. The pathological picture although typical for chronic encephalitis is nonspecific. The distribution of the changes, however, with exclusive involvement of one hemisphere, is typical for Rasmussen's encephalitis (3). Contralateral cerebellar atrophy has been reported in one autopsied case (3). In that case as well as in ours, the cerebellar atrophy could in part be explained by a combination of anterograde crossed cerebellar atrophy, by way of the cerebropontine tracts (4), and retrograde crossed cerebellar atrophy, by way of the thalamus and superior cerebellar peduncle (5). Additional factors, such as postictal cerebellar sclerosis could also be responsible for the cerebellar atrophy.

The etiology of Rasmussen's encephalitis is unknown but viral infection and autoimmunity have been implicated. The autoimmune hypothesis has attracted most attention after the finding that seizures and a chronic encephalitis develop in rabbits immunized with a portion of the aminoterminal region of glutamate receptor subunit GluR3. Following this observation circulating IgG antibodies directed against GluR3 were found in several patients with active Rasmussen's encephalitis but not in controls (6). Although the above findings raise an interesting connection between autoimmunity and Rasmussen's encephalitis the pathophysiological mechanisms leading to encephalitis are not clear.

The treatment of choice is functionally complete hemispherectomy with complete disconnection of the frontal and occipital lobes (7, 8).